Armored Scale

Armored scales develop through three life stages : egg, nymph, and adult, and the appearance of a stage can change as it ages. Adults are 1/8 inch or smaller, flattened, and rounded to irregular shaped. The body of armored scales rests beneath a plate-like cover that during most of the settled, development stages can be lifted off to reveal the insect body underneath. The coloration, shape, and microscopic features of the body and sometimes the cover and host distinguish the species of armored scale. However, some armored scale species cannot be determined by cover appearance due to similarity with other species. Armored scales lack wings and obvious body parts except for adult males that are not commonly observed and appear not to exist in certain species.

Most armored scales lay eggs that hatch beneath the cover of mature females; in some species eggs hatch within the female. The newly hatched immature scales, known as crawlers, are oval to rounded, orangish to yellow, and less than 1/25 inch (1 mm) long. They are mobile and may take up to 1 or 2 days to locate a suitable feeding site. Crawlers are also spread by wind or as contaminants on equipment, propagation tools, or people. After settling to feed they remain in the same spot and do not move. Unlike most other types of scales that feed on phloem sap, armored scales feed mostly on parenchyma tissue and do not produce honeydew. Most armored scales have several generations a year.

High populations of certain armored scales are associated with plant dieback and decline and may kill young plants. One exception is oleander scale, which appear to only minimally affect plant health even when very numerous. When abundant, the numerous, tiny scale covers can give infested plant parts a crusty brownish, grayish, or yellowish appearance. The salivary secretions of certain armored scales, such as San Jose scale, can cause discolored spots or streaks and severe growth distortion of some hosts.

Biological and cultural controls and the application of insecticides are the major management methods for armored scales.

Scale predators include brown lacewings, green lacewings, multicolored Asian lady beetle, Rhyzobius spp. lady beetles, and twicestabbed lady beetle. Parasitic wasps generally are the most important natural enemies of armored scales, including Aphytis, Comperiella, and Encarsia spp. Aphytis melinus is a naturally occurring and commercially available parasites that can be released to effectively control California red scale infesting citrus. For natural enemies to be effective, avoid application of persistent, broad-spectrum insecticides. Control ants, keep growing areas clean, and prevent dusty conditions, which impair the activity of natural enemies. Rely on cultural, mechanical, and selective chemical controls that do not kill parasites and predators or interfere with their beneficial activities. For more information, see Biological Control, Protecting Natural Enemies and Pollinators, and Natural Enemy Releases for Biological Control of Crop Pests.

Start crop production with uninfested stock and introduce only pest-free plants into growing areas. Dispose of heavily infested plants and crop debris in covered containers. Begin the work day in uninfested growing areas and keep containers, equipment, hands, and tools clean to minimize moving scale crawlers to other plants. Exclude windblown crawlers by covering greenhouse openings with fine mesh screens of sufficient surface area to allow adequate ventilation. On woody plants some use a strong spray of water to remove scales. This can help expose any remaining scales to subsequent treatment.

Biological and cultural controls are organically acceptable management methods. The botanical insecticide neem and certain oils (Organic JMS Stylet Oil) are also organically compatible.

Carefully inspect new plants before introducing them into production areas to ensure that they are free of scales and other pests. Quarantine new plants in separate growing areas until they have grown some and been periodically inspected for pests. Rogue or effectively treat infested plants.

Visually inspect plants at regular intervals to locate infestations, identify any scale species present, and help you decide when control is likely to be most effective. Insecticide application is generally warranted when scales are present and most crawlers (the stage most susceptible to insecticide) have emerged.

Armored scales may have multiple generations that overlap, with crawlers that emerge over a lengthy period. In this case multiple insecticide applications are commonly warranted to provide satisfactory control. First-generation crawler emergence earlier in the growing season generally occurs over a shorter time period, so treating early can reduce the total number of needed applications. To monitor crawler activity for timing applications, use traps of double-sided sticky tape wrapped around green stems or twigs in late winter near where female scales are observed. See Monitoring with Sticky Tape Traps for how to use this technique.

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